It is known that in some medical procedures, such as inter- and postoperative autotransfusion, there is a need to collect or salvage the blood lost by the patient to make it available for reinfusion back into the patient. Prior to reinfusion, the collected or salvaged blood typically needs to be separated and washed to make the blood safer for the patient. Specifically, the red blood cells need to be separated from the plasma which contains high levels of undesired elements such as activated clotting proteins, anticoagulant, activated platelets, coagulation by-products, cellular debris and free hemoglobin (Hgb). The removal of the free Hgb is desirable because at high levels it is toxic and can cause kidney damage. The removal of cellular debris, such as broken cell membranes, is also desirable because it may cause blood clotting and/or kidney necrosis.
It is known that through an autotransfusion system the patient's blood can be recovered by devices that comprise a blood reservoir to collect the salvaged blood, a centrifuge bowl or cell, which separates, concentrates and washes the red blood cells from the other blood components, and a reinfusion pouch or bag in which the washed and concentrated red blood cells are made available for reinfusion to the patient.
It is known that the procedure for the separation of blood components is generally performed in centrifuge bowls and usually comprises three steps. The first step is generally known as the filling step and is performed by filling the centrifuge bowl through an inlet tube. The centrifugal force created by the rotation of the centrifuge bowl, causes the red blood cells, which are the heaviest cellular components of blood, to be propelled outward, compacting against the wall of the centrifuge bowl. Other cellular components such as white blood cells and platelets are arranged in a thin layer known as a buffy coat directly adjacent to the mass of compacted red blood cells. The separated plasma which contains the undesired elements is the remaining component of blood and is arranged in a layer which lies above the buffy coat. As filling continues, more and more of the heavier blood components, i.e. the red blood cells, are pushed upwardly along a circumferential wall of the bowl until the lighter plasma is discharged through an outlet at the top of the centrifuge bowl. Once the centrifuge bowl has substantially filled with red blood cells, the filling step ends and the introduction of new blood into the centrifuge bowl ceases.
The above-described filling step is followed by a washing step which is performed to remove plasma and other unwanted blood components that have become trapped between the red blood cells. This is accomplished by the passing of a washing solution, which is usually saline, into the centrifuge bowl. The washing solution, when introduced into the centrifuge bowl, is usually added at a steady flow rate and gradually takes the place of the plasma and other unwanted elements, thus expelling them from the centrifuge bowl. At the end of the washing step the centrifuge bowl contains mainly red blood cells and washing solution, i.e., substances suitable to be reinfused to the patient. The contents of the cell are collected in a reinfusion pouch or bag in a third step of the procedure, known as emptying. This reinfusion pouch can then be made available for reinfusion to the patient.
Proper control of the washing step is important to ensure that free Hgb and other undesirable components are adequately removed before the blood is reinfused into the patient. Although it is difficult to detect the presence or absence of cellular debris, anticoagulant and other undesirable elements in the salvaged blood, it is easy to detect the presence or absence of free Hgb due to its reddish color. Free Hgb levels are relatively easy to measure experimentally and free Hgb washout is proven to correlate well with washout of other undesirable elements. Therefore, it is common practice to concentrate on free Hgb washout in the salvaged blood since the other undesirable elements will also be washed out. U.S. Pat. No. 5,478,479 to Herrig describes a system that uses a free Hgb sensor in the waste line from the centrifuge bowl to monitor the level of free Hgb. Care must be used during the washing step to avoid the spilling of red blood cells (RBC's) into the waste line. The Herrig patent proposes to avoid RBC spilling by reducing the speed of the pump which pumps washing solution into the centrifuge bowl if the sensor in the waste line detects RBC's. See column 6, lines 12 to 19. However, Herrig does not suggest increasing the speed of the pump if the sensor does not detect RBC's. It would be desirable to have a method and apparatus which minimize RBC spilling and which optirmize the time and the quality of the global washing step.